Materials having high dielectric constants have been researched for use as dielectric layers for thin film capacitors. As microelectronic circuits become increasingly integrated, the demand for smaller components becomes stronger. The quest for miniaturization is particulary ardent with regard to DRAM cell designs and devices. The migration of integrated circuits to smaller feature sizes is driving interest in developing thin film dielectrics having a dielectric constant (.epsilon.) greater than that of previously used materials. For example, typically films of a-SiO.sub.x have been used as a dielectric material in DRAM capacitors or capacitors of integrated-circuit devices. As the cell size has shrunk, designers have resorted to use of extremely thin a-SiO.sub.x films, but such films exhibit a decreased reliability due to their finite breakdown fields. Thus, efforts have been directed toward developing new dielectric materials. The inherent limitations of a-SiO.sub.x films may be avoided by substituting a material having a higher dielectric constant and comparable breakdown field.
Attention has been focused on materials with high values of .epsilon. and figure of merit, he figure of merit being the multiple of the dielectric constant (.epsilon.) and breakdown field (E.sub.br) of a material. In other words, the dielectric constant (.epsilon.) times the breakdown field (E.sub.br) MV/cm! equals its figure of merit (.epsilon.E.sub.br) .mu.C/cm.sup.2 !. The figure of merit is a useful unit of measure of the efficacy of a dielectric material, as it is not dependent upon film thickness.
In any case, use of a-Ta.sub.2 O.sub.5 (amorphous tantalum pentoxide), a-TiO.sub.x, and crystalline x-(Ba,Sr)TiO.sub.3, as dielectric materials has received particular attention. Each of these materials offers advantages and disadvantages. For example, the relatively high dielectric constant and large figure of merit for a-TaO.sub.x films have made them of particular interest. However, it is desirable to have dielectric films for use in integrated circuits with even higher dielectric constants (and breakdown fields), which has spurred interest in materials such as a-TiO.sub.x and x-(Ba,Sr)TiO.sub.3. On the other hand, while a-Ta.sub.2 O.sub.5 and a-TiO.sub.x incorporate elements that are generally considered compatible with integrated circuit fabrication, Ba and Sr are more problematic. Thus, a material having a high dielectric constant and compatibility with silicon-chip integrated circuit fabrication would be useful.
Accordingly, there is a need for a dielectric material for use in an integrated circuit device equipped with a capacitor having high dielectric constants, large breakdown fields, and compatibility with silicon-chip integrated circuit fabrication. Applicants have discovered that thin amorphous films of R--Sn--Ti--O are useful for this purpose, where R is selected from the group consisting of zirconium (Zr) and hafnium (Hf).
Zr--Ti--Sn--O ceramics--in crystalline or polycrystalline form--previously have been reported as useful for their microwave properties, including a moderate dielectric constant and low temperature coefficient of permittivity. However, the compositions previously studied are typical of those used in such applications, that is, they invariably fall within a homogeneous phase field. Thin films of (Zr,Sn)TiO.sub.4 have been reported as useful as components of dielectrics for capacitors of hybrid integrated circuits. See O. Nakagawara, Y. Toyoda, M. Kobayashi, Y. Yoshino, Y. Katayama, H. Tabata, and T. Kawai, "Electrical Properties of (Zr,Sn)TiO.sub.4 Dielectric Thin Film Prepared by Pulsed Laser Deposition," J. APPL. PHYS. 80, 388 (1996) ("Nakagawara"). However, Nakagawara reports a relative decrease in the dielectric constant for amorphous films, attributing this decrease to a decrease in the ionic polarizability of the materials. The films reported by Nakagawara are structurally close to crystalline x-(Zr, Sn)TiO.sub.4, following prior art teachings directed toward compositions falling within homogeneous crystalline phase fields, and they report films having dielectric constants of about .epsilon.=22.
Applicants have discovered, however, that materials having an amorphous composition of zirconium-tin-titanium-oxide or hafnium-tin-titanium-oxide, falling outside the homogeneous crystalline phase fields typically considered optimum, are advantageous as thin dielectric materials so that the area of the capacitor can be substantially reduced. Applicants have further discovered as preferred dielectric materials of the composition (Zr..sub.2 Sn..sub.2 Ti..sub.6).sub.2 O.sub.x N.sub.v having a dielectric constant of about 61 and a breakdown field of 4.1 MV/cm, when deposited on a substrate held at 200 degrees Centigrade. This reflects a figure of merit .epsilon.E.sub.br =22.1 .mu.C/cm,.sup.2 which is about threefold higher than that of the best a-TaO.sub.x films and about sevenfold higher than that of high-quality deposited a-SiO.sub.x films. Additionally, the films disclosed herein are relatively stable and survive conventional back-end processing steps used in silicon integrated-circuit fabrication.